The present invention relates to a drive unit and in particular, an electromotive window-lift drive for a motor vehicle.
The German Patent Application DE-U-83 23 218 discusses an electromotive window-lift drive for a motor vehicle having a traversing drive shaft, which accommodates the laminated core of the rotor and the commutator of a commutator motor inside a motor housing. A worm gear which mates with a worm wheel is accommodated in an adjacent gear housing. The drive shaft is supported at each of its outer shaft ends by a cup-shaped bearing located in the gear housing and the motor housing, respectively. The axial forces acting by way of the worm gear on the drive shaft are absorbed in one direction of rotation by an axial-play adjusting screw in the gear housing and, in a second direction, by the flat abutment surface of the front end of the motor housing running perpendicularly to the axis of the drive shaft. The front ends of the drive shaft run up against this abutment surface, preferably via a thrust mushroom-type head.
Besides the axial force already mentioned, radial forces and tangential forces develop at the worm gear toothing and also act on the drive shaft. The total force resulting from these two forces causes a slight elastic deformation of the shaft. The extent of the elastic deformation of the shaft may be such that the front-end, thrust mushroom-type heads of the drive shaft drift are eccentrically displaced on the housing-side outer bearings.
In particular, if the bearing arrangement provided for the drive shaft comprises two bearings on the side of the worm shaft (i.e., in the gear-housing) and an overhung bearing arrangement results for the motor-side, unsupported and unattached (i.e., free) shaft end, when this shaft end abuts against the flat abutment surface of the motor housing, the unattached shaft end may be bent eccentrically to such an extent that a collision can occur between the laminated core of the rotor accommodated by the drive shaft and the diametrically opposed magnet segments of the stator in the air-gap space. To prevent such a collision, the drive shaft requires thicker dimensions or must be provided with additional support means to protect it from bending out radially--such as in the case of the German Utility Model DE-U-81 28 186.
Therefore, there is a need to minimize an eccentric bending of the unsupported and unattached (i.e., free) motor-side shaft end of the drive shaft using simple construction and assembly-technology means.